Combustion Of Lithium At Different Temperatures And Pres-sures And With Gas Surpluses Using Porous Tubes As Burners

ABSTRACT

A method is provided for combusting a metal M, selected from alkali, alkaline earth metals, aluminum, and zinc, and alloys and/or mixtures thereof, using a combustion gas. The combustion is performed using a porous burner including a porous tube as the burner. A device for performing such method is also disclosed, as well as the use of a porous burner including a porous tube as the burner for combusting the metal M using the combustion gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/EP2015/059724 filed May 4, 2015, which designates the United States of America, and claims priority to DE Application No. 10 2014 209 529.8 filed May 20, 2014, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a process for combusting a metal M selected from alkali metals, alkaline earth metals, aluminum and zinc, and alloys and or mixtures thereof, with a fuel gas, wherein the combustion is effected by means of a pore burner comprising a porous tube as burner, to an apparatus for conducting the process and to the use of a pore burner comprising a porous tube as burner for combustion of a metal M selected from alkali metals, alkaline earth metals, aluminum and zinc, and alloys and or mixtures thereof, with a fuel gas.

BACKGROUND

Over the years, a multitude of energy generation units which work with heat generated in the oxidation of metallic lithium have been proposed (e.g. U.S. Pat. No. 3,328,957). In such a system, water and lithium are reacted with one another to produce lithium hydroxide, hydrogen and steam. Elsewhere in the system, the hydrogen produced by the reaction between lithium and water is combined with oxygen to form additional steam. The steam is then used to drive a turbine or the like, and so an energy generation source is obtained. Lithium can also be used additionally to obtain commodity materials. Examples are the reaction with nitrogen to give lithium nitride and subsequent hydrolysis to give ammonia or with carbon dioxide to give lithium oxide and carbon monoxide. The solid final end product of the reaction of lithium in each case, optionally after hydrolysis, as in the case of nitride, is the oxide or carbonate, which can then be reduced again by means of electrolysis to lithium metal. This establishes a circuit in which, by means of wind power, photovoltaics or other renewable energy sources, surplus power can be produced, stored and converted back to power at the desired time, or else chemical commodity materials can be obtained.

Lithium is typically produced by melt flow electrolysis. For this process, efficiencies of about 42%-55% are found, calculated from process data without temperature correction of the standard potential. As well as lithium, it is also possible to use similar metals such as sodium, potassium, magnesium, calcium, aluminum and zinc.

Since solid or liquid residues can arise in the combustion of lithium, according to the temperature and fuel gas, particular attention should be paid to these. Moreover, according to the construction and operation of an oven for the combustion of lithium metal (for example in liquid form) in different atmospheres and under pressure, offgases and solids/liquids can arise as combustion products. These solid and liquid substances have to be very substantially separated from the offgases.

Substantially complete separation of liquid and solid combustion residues from the offgas stream is important in order not to generate any surface deposits or blockages in the downstream apparatuses. More particularly, it is very demanding to guide the offgas stream directly to a gas turbine, since it has to be ensured in that case that all particles have been completely removed from the offgas stream. Such particles cause long-term damage to the gas turbine blades and lead to failure of the plant.

SUMMARY

One embodiment provides a process for combusting a metal M selected from alkali metals, alkaline earth metals, aluminum and zinc, and alloys and/or mixtures thereof, with a fuel gas, wherein the combustion is effected by means of a pore burner comprising a porous tube as burner.

In one embodiment, the pore burner is supplied with the metal M in liquid form in the interior of the pore burner.

In one embodiment, the fuel gas is guided onto the outer surfaces of the pore burner and combusted with the metal M.

In one embodiment, the combustion takes place at a temperature above the melting point of the salts formed in the reaction of metal M and fuel gas.

In one embodiment, the metal M is supplied as an alloy of at least two metals M.

In one embodiment, the reaction products are separated after the combustion.

In one embodiment, the separation is effected with the aid of a cyclone.

In one embodiment, the reaction products of the combustion are used to generate energy, preferably using at least one expander turbine and/or at least one gas turbine and/or at least one heat exchanger and/or at least one boiler.

Another embodiment provides an apparatus for combustion of a metal M selected from alkali metals, alkaline earth metals, aluminum and zinc, and alloys and/or mixtures thereof, comprising a pore burner comprising a porous tube as burner, a feed unit for a metal M, preferably in liquid form, to the interior of the pore burner, which is designed to feed the pore burner with the metal M, preferably in liquid form, a feed unit for a fuel gas, which is designed to supply fuel gas, and optionally a heating apparatus for providing the metal M in liquid form, which is designed to liquefy the metal M.

In one embodiment, the feed unit for the fuel gas is arranged such that it guides the fuel gas at least partly to the surface of the pore burner.

In one embodiment, the pore burner is arranged such that reaction products that form from the combustion and optionally the metal M can be removed by gravity from the surface of the pore burner.

In one embodiment, the pore burner consists of a material selected from the group consisting of iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zirconium and alloys of these metals, and also steels such as stainless steel and chromium-nickel steel.

In one embodiment, the apparatus further comprises a separation unit for the products of the combustion of the metal M, which is designed to separate the combustion products of the metal M and the fuel gas, the separation unit preferably being a cyclone reactor.

In one embodiment, the apparatus further comprises at least one expander turbine and/or at least one gas turbine and/or at least one heat exchanger and/or at least one boiler.

Another embodiment provides for the use of a pore burner comprising a porous tube as burner for combustion of a metal M selected from alkali metals, alkaline earth metals, aluminum and zinc, and alloys and/or mixtures thereof, with a fuel gas.

BRIEF DESCRIPTION OF THE DRAWINGS

Example aspects and embodiments of the present invention are described below with reference to the drawings, in which:

FIG. 1 shows, in schematic form, an illustrative arrangement for an apparatus of the invention.

FIG. 2 shows, in schematic form, a detail view in a further illustrative arrangement for an apparatus of the invention.

FIG. 3 shows, in schematic form, a further detail view in an additional illustrative arrangement for an apparatus of the invention.

FIG. 4 shows, in schematic form, an illustrative cross section through an illustrative apparatus of the invention in the region of the feed unit of the carrier gas to the reactor.

FIG. 5 shows a scheme for an illustrative reaction of lithium and carbon dioxide to give lithium carbonate, which can be conducted by the process according to the invention.

FIG. 6 shows a scheme for a further illustrative reaction of lithium and nitrogen to give lithium nitride and further conversion products, which can be conducted by the process according to the invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide a process and an apparatus with which efficient removal of solid and/or liquid reaction products from the offgas can be effected in the case of combustion of a metal M selected from alkali metals, alkaline earth metals, Al and Zn, and alloys and mixtures thereof, with a fuel gas. Other embodiments provide an apparatus with which effective and locally limited combustion of the metal M with the fuel gas is enabled, without too much distribution of the combustion products in the combustion space and hence easier removability thereof. Other embodiments provide a use of such apparatus to effectively control the combustion of the metal M with the fuel gas.

Some embodiments provide a pore burner comprising a porous tube as burner, in the combustion of the metal M with the fuel gas. It has been found that it is possible through the use of the pore burner to localize the combustion at the pore burner, in which case the combustion products are also obtained at the pore burner. Whereas, for example, in the case of atomization the reaction products are obtained throughout the reactor and solid and liquid reaction products have to be separated again in a complex manner from gaseous reaction products, in the case of combustion with the pore burner there is localization of solid and liquid reaction products in particular close to the pore burner, which facilitates separation thereof from gaseous combustion products. In this way, the entire combustion apparatus can also be made more compact and the combustion can be configured so as to be gentler in respect of the apparatus through localization of the combustion process.

Some embodiments provide a process for combusting a metal M selected from alkali metals, alkaline earth metals, aluminum and zinc, and alloys and/or mixtures thereof, with a fuel gas, wherein the combustion is effected by means of a pore burner comprising a porous tube as burner.

Other embodiments provide an apparatus for combustion of a metal M selected from alkalimetals, alkaline earth metals, aluminum and zinc, and alloys and/or mixtures thereof, comprising a pore burner comprising a porous tube as burner, a feed unit for a metal M, preferably in liquid form, to the interior of the pore burner, which is designed to feed the pore burner with the metal M, preferably in liquid form, a feed unit for a fuel gas, which is designed to supply fuel gas, and optionally a heating apparatus for providing the metal M in liquid form, which is designed to liquefy the metal M.

Other embodiments provide the use of a pore burner comprising a porous tube as burner for combustion of a metal M selected from alkali metals, alkaline earth metals, aluminum and zinc, and alloys and/or mixtures thereof, with a fuel gas.

One embodiment provides a process for combusting a metal M selected from alkali metals, alkaline earth metals, aluminum and zinc, and alloys and/or mixtures thereof, with a fuel gas, wherein the combustion is effected by means of a pore burner comprising a porous tube as burner.

The metal M, in particular embodiments, is selected from alkali metals, preferably Li, Na, K, Rb and Cs, alkaline earth metals, preferably Mg, Ca, Sr and Ba, Al and Zn, and mixtures and/or alloys thereof. In preferred embodiments, the metal M is selectedfrom Li, Na, K, Mg, Ca, Al and Zn, further preferably Li and Mg, and the metal M is more preferably lithium. Useful fuel gases, in particular embodiments, are those which can react with the metal M mentioned or mixtures and/or alloys of the metals M in an exothermic reaction, although these are not particularly restricted. By way of example, the fuel gas may comprise air, oxygen, carbon dioxide, hydrogen, water vapor, nitrogen oxides NO_(x) such as dinitrogen monoxide, nitrogen, sulfur dioxide, or mixtures thereof. The process can thus also be used for desulfurization or NO_(x) removal. According to the fuel gas, it is possible here to obtain various products with the various metals M, which may be in solid, liquid or else gaseous form.

For example, a reaction of metal M, for example lithium, with nitrogen can give rise, inter alia, to metal nitride, such as lithium nitride, which can then be allowed to react further at a later stage to give ammonia, whereas a reaction of metal M, for example lithium, with carbon dioxide can give rise, for example, to metal carbonate, for example lithium carbonate, carbon monoxide, metal oxide, for example lithium oxide, or else metal carbide, for example lithium carbide, or else mixtures thereof, it being possible to use the carbon monoxide to obtain higher-value products, for example including longer-chain carbonaceous products such as methane, ethane, etc., up to and including benzine, diesel, but also methanol etc., for example in a Fischer-Tropsch process, whereas it is possible to use metal carbide, for example lithium carbide, to obtain acetylene, for example. In addition, for example, it is also possible with dinitrogen monoxide as fuel gas to form metal nitride, for example.

Analogous reactions can also arise for the other metals mentioned. According to the invention, the pore burner is not particularly restricted, provided that it comprises a porous tube as burner, which can be supplied at at least one orifice with the metal M. Preferably, the metal M is supplied only through one orifice of the tube and the other end of the tube is closed or likewise consists of the material of the porous tube. The porous tube here may, for example, be a ceramic tube made of aluminum oxide or magnesium oxide or a porous metal tube, for example made of iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zirconium and alloys of these metals, and also steels such as stainless steel and chromium-nickel steel. The pore burner preferably consists of a material selected from the group consisting of iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zirconium and alloys of these metals, and also steels such as stainless steel and chromium-nickel steel. Suitable examples are austenitic chromium-nickel steels which are very resistant, for example, to erosion by sodium at high temperature, but materials having 32% nickel and 20% chromium, such as AC 66, Incoloy 800 or Pyrotherm G 20132 Nb also exhibit relatively favorable corrosion characteristics. The further constituents of the pore burner are not subject to any further restriction and may comprise the feed unit for the metal M and optionally an ignition source, etc.

In particular embodiments, the metal M is guided in liquid form into the pore burner and combusted with the aid of the pore burner, wherein the fuel gas is optionally guided to the outer surfaces of the pore burner and combusted with the metal M. However, no internal mixing takes place as in a conventional pore burner in particular embodiments, in order to avoid blockage of the pores by solid reaction products. In particular embodiments, the pore burner is thus a pore burner without internal mixing. In the case of use of the pore burner in particular embodiments, the pores serve solely to increase the surface area of the alloy L. In the case of continuous supply of the alloy L of the electropositive metal, however, a reaction with the fuel gas can take place at the exit of the pores close to the surface of the pore burner, provided that it can be ensured that reaction products that form are conveyed out of the pore burner by further delivery of alloy L. In particular embodiments, however, the combustion reaction takes place outside the pores of the pore burner, for example at the surface of the pore burner or even after exit of the alloy L from the pore burner, i.e. only at the surface of the exiting alloy L.

In particular embodiments, the pore burner is supplied with the metal M in liquid form in the interior of the pore burner. This leads to better distribution of the metal M in the pore burner and more homogeneous exit of the metal from the pores of the porous tube, such that a more homogeneous reaction can take place between metal M and fuel gas. The combustion of metal M and fuel gas can be suitably controlled, for example, via the pore size of the pores of the tube, the metal M used, the density thereof, which can be correlated to the temperature of the metal M, the pressure with which the metal M is introduced into the pore burner, the pressure or the application/feed rate of the fuel gas, etc. The metal M, for example lithium, in particular embodiments, is accordingly used in liquid form, i.e., for example, above the melting point of lithium of 180° C. The liquid metal M can be injected here into the porous tube, for example also with the aid of a further gas under pressure, which is unrestricted. The liquid metal M then passes through the pores of the tube to the surface and burns with the gas to give the respective reaction product(s).

In particular embodiments, the fuel gas is guided to the outer surfaces of the pore burner and combusted with the metal M. This can reduce or prevent blockage of the pores of the porous tube, such that cleaning of the pore burner is prevented or else wear can be reduced.

The combustion of the metal M at the surface of the porous tube reduces the tendency for passage of small particles into the gas space/reaction space, such that, at best, relatively large droplets of reaction products arise, but these can be easily separated from gaseous reaction products, for example be deposited onto the reactor wall by means of a cyclone. In this case, the reactor wall can be cooled, for example with heat exchangers, in which case these may also be connected to turbines and generators.

In particular embodiments, the combustion is effected at a temperature above the melting point of the salts formed in the reaction of metal M and fuel gas. The salts formed in the combustion of metal M and fuel gas may have a melting point here above the melting point of the metal M, such that supply of liquid metal M at elevated temperature may be required. The combustion at a temperature above the melting point of the salts formed can additionally avoid contamination or coverage of the pore burner by the salts formed, such that the pore burner can be better protected against contamination, for example of the pores as well. This enables better operation and reduced cleaning of the apparatus, and also longer use times without cleaning. It is also possible for liquid reaction products to simply drip off the burner. Especially in the case of those processes at temperatures above the melting point of the salts formed, preferred materials for the burner are those that can withstand the temperatures, for example iron, niobium, tantalum, molybdenum, tungsten, zirconium and alloys of these metals, and stainless steel.

The combustion temperature is thus preferably higher than the melting point of the respective reaction product(s), in order that the pores of the pore burner are not blocked and the reaction products can be transported away. In addition, according to the reaction product, a certain degree of mixing between the liquid metal M and the reaction product can take place, such that the combustion can take place not only locally at the pore opening, but distributed over the entire surface of the tube. This can be controlled, for example, via the feed rate of the metal M.

In particular embodiments, the metal M is supplied to the pore burner as an alloy of at least two metals M. In this way, it is possible to achieve melting point depression of the metal M, and also of the metal salt(s) formed, such that the process can be conducted at lower temperatures and hence in a gentler manner in respect of the apparatus, and the use of highly refractory materials in the apparatus can be reduced or avoided.

In addition, in particular embodiments, the combustion can be effected with a certain excess of fuel gas, for example in a molar ratio of fuel gas to metal M of 1.01:1 or more, preferably 1.05:1 or more, further preferably 5:1 or more, even further preferably 10:1 or more, for example even 100:1 or more, in order to stabilize the offgas temperature within a particular temperature range. The fuel gas can also serve here for removal of heat in the expander portion of a turbine etc.

In the process, a separation of offgas from solid and/or liquid reaction products can additionally be effected in the case of combustion of the metal M with a fuel gas, in which case, in particular embodiments, in a reaction step, the fuel gas is combusted with the metal M and offgas and further solid and/or liquid reaction products are formed, and, in a separation step, the offgas is separated from the solid and/or liquid reaction products. In this case, in the separation step, a carrier gas can additionally be added and the carrier gas can be removed as a mixture with the offgas. The carrier gas here may also correspond to the offgas, such that, for example, the combustion gives rise to an offgas corresponding to the carrier gas supplied, or else may correspond to the fuel gas. In the process of the invention, it is thus possible, in particular embodiments, to separate the reaction products after the combustion.

In some embodiments, the carrier gas is not particularly restricted, and may correspond to the fuel gas, but may also be different therefrom. Carrier gases employed may, for example, be air, carbon monoxide, carbon dioxide, oxygen, methane, hydrogen, water vapor, nitrogen, dinitrogen monoxide, mixtures of two or more of these gases, etc. It is possible here for various gases, for example methane, to serve for heat transport and remove the heat of reaction of the reaction of metal M with the fuel gas from the reactor. The various carrier gases can, for example, be suitably matched to the reaction of the fuel gas with the metal M, in order possibly to achieve synergistic effects here. The gas which is optionally used in the supply of the metal M may likewise correspond to the carrier gas.

For combustion of carbon dioxide with metal M, for example lithium, where carbon monoxide can form, the carrier gas used may, for example, be carbon monoxide and may optionally be circulated, i.e. at least partly recycled again as carrier gas after removal. In this case, the carrier gas is matched to the offgas, such that a portion of the carrier gas can optionally be withdrawn as product of value, for example for a subsequent Fischer-Tropsch synthesis, while it is regenerated by the combustion of carbon dioxide with metal M, such that there is at least partial conversion of carbon dioxide to carbon monoxide overall, preferably to an extent of 90% by volume or more, further preferably 95% by volume or more, even further preferably 99% by volume or more and especially preferably to an extent of 100% by volume, based on the carbon dioxide used, and is withdrawn as product of value. The more carbon monoxide is generated, the cleaner the carbon monoxide removed. In the case of combustion of nitrogen with metal M, for example lithium, the carrier gas used may, for example, be nitrogen, such that unreacted nitrogen in the offgas from the combustion may be present as “offgas” alongside the nitrogen carrier gas, as a result of which a separation of gas, if desired, can be conducted in a simpler manner and, in particular embodiments, in the case of appropriate, preferably quantitative, combustion of metal M and nitrogen using suitable, easily determinable parameters, may even not be required. It is possible, for example, to easily remove ammonia from the nitride formed by scrubbing or cooling.

In particular embodiments, at least a portion of the offgas may correspond to the carrier gas. For example, the offgas may correspond to the carrier gas to an extent of at least 10% by volume, preferably 50% by volume or more, further preferably 60% by volume or more, even further preferably 70% by volume or more, and even more preferably 80% by volume or more, based on the total volume of the offgas. In particular embodiments, the fuel gas may correspond to the carrier gas to an extent of 90% by volume or more, based on the total volume of the offgas, and may in some cases even correspond to the carrier gas to an extent of 100% by volume.

In particular embodiments, in the process of the invention, the mixture of offgas and carrier gas can be supplied at least partly back to the separation step as carrier gas and/or to the combustion step as fuel gas. Recycling of the mixture of offgas and carrier gas can be effected, for example, to an extent of 10% by volume or more, preferably 50% by volume or more, further preferably 60% by volume or more, even further preferably 70% by volume or more, and even more preferably 80% by volume or more, based on the total volume of carrier gas and offgas. In particular embodiments, recycling of the mixture of offgas and carrier gas can be effected to an extent of 90% by volume or more, based on the total volume of carrier gas and offgas. In embodiments that are preferred in accordance with the invention, a reaction between fuel gas and metal M can be effected in such a way that the offgas formed is the carrier gas, for example with carbon dioxide as fuel gas and carbon monoxide as carrier gas, such that the mixture of carrier gas and offgas then consists essentially of the carrier gas, preferably to an extent of 90% by volume or more, further preferably to an extent of 95% by volume or more, even further preferably to an extent of 99% by volume or more and more preferably to an extent of 100% by volume, based on the mixture of offgas and carrier gas. In this case, the carrier gas can then be continuously circulated and withdrawn in such an amount as it is reformed by the combustion of metal M and fuel gas. Compared to pure cycling of the carrier gas, where a separation of carrier gas and offgas is optionally effected, it is possible here, for example, to obtain a product of value, for example carbon monoxide, which can be withdrawn continuously.

In particular embodiments, the separation step in a process of the invention is effected in a cyclone or a cyclone reactor. The cyclone reactor here is not particularly restricted in terms of its setup and may, for example, have a form as possessed by standard cyclone reactors.

For example, a cyclone reactor may comprise a reaction region to which there may be connected feed units for the fuel gas, metal M and the carrier gas (which may optionally also be combined beforehand and then supplied together to the reaction region), for example in the form of a rotationally symmetric upper section, a separation region which has a conical configuration, for example, and an expansion chamber to which there may be connected a removal apparatus for solid and/or liquid reaction products from the combustion of metal M with the fuel gas, for example in the form of a star feeder, and a removal unit for the mixture of offgas and carrier gas, which arises after the mixing of the two gases after the combustion of the metal M in the fuel gas.

Such apparatus components are, for example, typically present in cyclone separators. A cyclone reactor used in accordance with the invention may alternatively have a different construction and may optionally also comprise further regions. For example, individual regions (e.g. reaction region, separation region, the expansion chamber) may also be combined in one component of an illustrative cyclone reactor and/or extend over two or more components of a cyclone reactor. It is possible here, for example, for carrier gas also to be added in a region in which the reaction of the metal M and the fuel gas is advanced or even already complete.

By virtue of the cyclone, the reaction products are kept largely in the center of the reactor, for example of a furnace space, and, since the combustion at the surface of the porous tube does not give rise to any small particles as in the case of atomization, the offgas is free of solid or liquid particles, such that it is also possible to connect a gas turbine or expander turbine downstream within the offgas stream. Under these circumstances, it is possible with this combustion concept to introduce the offgas stream directly into a gas turbine after the combustion of the metal M and the separation of the reaction products.

The offgas temperature, in particular embodiments, in the different combustion processes, can be controlled via the excess of gas, such that it is higher than the melting temperature of the reaction products or mixture thereof. In particular embodiments, the cyclone reactor additionally comprises a grid, by means of which the solid and/or liquid reaction products can be removed in the combustion of the metal M with the fuel gas. Such a grid can additionally prevent subsequent vortexing of solid and/or liquid reaction products in the cyclone reactor.

The reaction products of the combustion can be used to generate energy, preferably using at least one expander turbine and/or at least one gas turbine, for example a steam turbine, and/or at least one heat exchanger and/or at least one boiler, for which it is possible here, in particular embodiments, to use both the solid and/or liquid reaction products formed, for example with use of a heat exchanger in the reactor, or else the gaseous reaction products.

In the case of use of a cyclone reactor with carrier gas supply, the mixture of offgas and carrier gas, in particular embodiments, for example in the reactor and/or in the case of and/or after removal from the reactor, can be used for heating of a boiler or for heat transfer in a heat exchanger or a turbine, for example a gas turbine or an expander turbine.

In addition, the mixture of the carrier gas and the offgas, in particular embodiments, may be under elevated pressure after the combustion, for example more than 1 bar, at least 2 bar, at least 5 bar or at least 20 bar.

Furthermore, in a further aspect of the invention, an apparatus for combustion of a metal M selected from alkali metals, alkaline earth metals, aluminum and zinc, and alloys and/or mixtures thereof is disclosed, comprising a pore burner comprising a porous tube as burner, a feed unit for a metal M, preferably in liquid form, to the interior of the pore burner, which is designed to supply the pore burner with the metal M, preferably in liquid form, a feed unit for a fuel gas, which is designed to supply fuel gas, and optionally a heating apparatus for providing the metal M in liquid form, which is designed to liquefy the metal M.

The pore burner may be configured here as described above. The feed unit used for metal M may, for example, be tubes or hoses, or else conveyor belts, which may be heated, which can be suitably determined, for example, on the basis of the state of matter of the metal M. Optionally, the feed unit for the metal M may also be connected to a further feed unit for a gas, optionally with a control unit such as a valve, with which the supply of the metal M can be regulated. It is likewise possible for the feed unit for the fuel gas to be configured as a tube or hose, etc., which may optionally be heated, in which case the feed unit can be suitably determined on the basis of the state of the gas, which may optionally also be under pressure. It is also possible for several feed units to be provided for metal M or fuel gas.

In particular embodiments, the feed unit for the fuel gas is arranged such that it guides the fuel gas, at least partly and preferably completely, to the surface of the pore burner. This achieves an improved reaction between metal M and fuel gas.

Moreover, the pore burner, in some embodiments, is arranged such that reaction products formed in the combustion and optionally the unreacted metal M can be removed from the surface of the pore burner by gravity, for example by virtue of the pore burner being mounted vertically in the reactor, pointing toward the surface of the earth. In the case of vertical arrangement of the porous combustion tubes in the furnace space, the liquid reaction product formed can run out of the tube and then drip downward into the furnace bottom. In this way, the possibly dissolved metal M, for example lithium, which has not reacted in the pore burner beforehand is also combusted, and the heat of reaction is released to the fuel gas and carrier gas flowing past.

In particular embodiments, the pore burner consists of a material selected from the group consisting of iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zirconium and alloys of these metals, and also steels such as stainless steel and chromium-nickel steel. These materials are preferred for use at relatively high temperatures, where the reaction with liquid metal M and optionally with liquid metal salts formed can take place in a simpler manner.

In particular embodiments, the apparatus of the invention may further include a separation unit for the products of the combustion of the metal M, which is designed to separate the combustion products of the metal M and of the fuel gas, the separation unit preferably being a cyclone reactor.

The separation unit may serve here for separation of offgas in the combustion of the metal M with a fuel gas, and may comprise:

-   -   a reactor in which the pore burner is provided and the feed unit         for metal M is mounted or provided, and to which the fuel gas is         supplied, i.e. to which or in which the feed unit for the fuel         gas is connected or provided;     -   a feed unit for carrier gas, which is designed to supply carrier         gas to the reactor;     -   a removal unit for a mixture of offgas and carrier gas, which is         designed to remove a mixture of the offgas from the combustion         of metal M with the fuel gas and the carrier gas; and a removal         unit for solid and/or liquid reaction products from the         combustion of metal M with the fuel gas, which is designed to         remove solid and/or liquid reaction products from the combustion         of metal M with the fuel gas.

The feed unit for carrier gas is likewise not particularly restricted and comprises, for example, tubes, hoses, etc., it being possible to suitably determine the feed unit for carrier gas on the basis of the state of the carrier gas, which may optionally also be under pressure.

The reactor is likewise not particularly restricted, provided that the combustion of the fuel gas with the metal M can take place therein. In particular embodiments, the reactor may be a cyclone reactor as shown by way of example in FIG. 1 and in detail view in a further embodiment in FIG. 2.

The cyclone reactor may, in particular embodiments, comprise a reaction region to which there may be connected feed units for the fuel gas, metal M and the carrier gas, and also the pore burner, for example in the form of a rotationally symmetric upper section, a separation region which has a conical configuration, for example, and an expansion chamber to which there may be connected a removal apparatus for solid and/or liquid reaction products from the combustion of metal M with the fuel gas, for example in the form of a star feeder, and a removal unit for the mixture of offgas and carrier gas, which arises after the mixing of the two gases after the combustion of the metal M in the fuel gas.

Such apparatus components are, for example, typically present in cyclone separators. A cyclone reactor used in accordance with the invention may alternatively have a different construction and may optionally also comprise further regions. For example, individual regions (e.g. reaction region, separation region, the expansion chamber) may also be combined in one component of an illustrative cyclone reactor and/or extend over two or more components of a cyclone reactor.

An illustrative cyclone reactor is shown in FIG. 1. The cyclone reactor 6 shown in FIG. 1 comprises a reaction region 20 a, a separation region 20 b which is both together with the reaction region 20 a in the upper component 6 a and together with the expansion chamber 20 c in the lower component 6 b, and an expansion chamber 20 c. Connected to the cyclone reactor in the upper section are a feed unit 1 for fuel gas, for example in the form of an optionally heated tube or a hose, and a feed unit 2 for metal M, for example in the form of an optionally heated tube or a hose, the metal M being supplied to the pore burner 3. According to FIG. 1, the metal M is fed in with the aid of a gas in a feed unit 2′ for gas, for example a tube or hose, the feed of which can be controlled with a valve 2″. The metal M and the fuel gas are fed to the reaction region 20 a. Through the feed unit 4, the carrier gas is supplied to a region 4′ for gas distribution, from which the carrier gas is then supplied to the separation region 20 b via nozzles 5 with which a cyclone can be formed. A detail view of such a feed unit 4 having a region 4′ for gas distribution and a nozzle 5 is specified in cross section, by way of example, in FIG. 4 (illustration without pore burner 3), but it is also possible for more nozzles 5 to be present, for example at a suitable distance in a ring around the inner wall of the region 4′, in order to generate a suitable cyclone. Solid and/or liquid reaction products are removed from the lower component 6 b comprising the expansion chamber 20 c via the removal unit 7 for solid and/or liquid reaction products of the combustion of metal M with the fuel gas, while the mixture of offgas and carrier gas is removed via the removal unit 8 for the mixture of offgas and carrier gas.

Optionally, in an apparatus of the invention, an ignition apparatus, for example an electrical ignition apparatus or a plasma arc, may be required, this being dependent on the nature and state of the metal M, for example the temperature and/or state of matter thereof, the characteristics of the fuel gas, for example the pressure and/or temperature thereof, and the arrangement of components in the apparatus, for example the nature and characteristics of the feed units.

In order to achieve, by means of construction, both a high offgas temperature of more than 200° C., for example even 600° C. or more, and in particular embodiments 700° C. or more, and an elevated (e.g. 5 bar or more) or high (20 bar or more) operating pressure, the internal reactor material may consist of alloys of high heat resistance, for example, in the extreme case, even of the material Haynes 214. Around this material, which is merely supposed to withstand the high temperature, it is then possible to arrange a thermal insulation which allows a sufficiently small amount of heat through, such that a steel wall on the outside, which may additionally also be air- or water-cooled, absorbs the compressive stress. The offgas can then be supplied to the further process step with the elevated or high operating pressure.

Furthermore, the reactor, for example a cyclone reactor, may also comprise heating and/or cooling apparatuses present in the reaction region, the separation region and/or the expansion chamber, and also in the various feed and/or removal apparatuses, optionally the burner, and/or optionally the ignition apparatus. Furthermore, further components such as pumps for generation of a pressure or a vacuum, etc. may be present in an apparatus of the invention. In embodiments in which the reactor takes the form of a cyclone reactor, the cyclone reactor may comprise a grid which is designed such that the solid and/or liquid reaction products can be removed through the grid on combustion of the metal M with the fuel gas. Furthermore, such a grid may alternatively also be present in other reactors which may be provided in the apparatus of the invention. The use of the grid in the reactor or cyclone reactor can achieve better separation of the solid and/or liquid reaction products in the combustion of the metal M with the fuel gas from the mixture of offgas and carrier gas. Such a grid is shown by way of example in FIG. 2, in which the grid 6′ is present by way of example in the cyclone reactor 6 shown in FIG. 1 in the lower component 6 b above the removal unit 7 and below the removal unit 8. By means of the grid, preferably with a sufficiently large distance from the reactor wall, it is possible to ensure reliable separation of solid and liquid reaction products or a mixture thereof. In this way, the already deposited solid or liquid combustion products are not vortexed by the cyclone either.

The geometry of the feed units for the carrier gas is not particularly restricted, provided that the carrier gas can be mixed with the offgas from the combustion of metal M and fuel gas. A cyclone preferably forms here, for example with the apparatus shown in FIG. 1. A cyclone can alternatively be generated by other arrangements of the feed units with respect to one another. For example, it is not impossible that the feed unit for the carrier gas is present at the top of the reactor close to the feed units for metal M and fuel. Correspondingly suitable geometries for the injection can easily be determined in a suitable manner, for example on the basis of flow simulations.

Nor are the removal units particularly restricted, it being possible, for example, for the removal unit for the mixture of offgas and carrier gas to be configured as a tube, while the removal unit for the solid and/or liquid reaction products of the combustion of metal M with the fuel gas may be configured, for example, as a star feeder and/or as a tube with a siphon. It is also possible here for various valves, such as pressure valves, and/or further regulators to be provided. An illustrative removal unit 7 shown in FIG. 3, for example of the cyclone reactor 6 shown in FIG. 1, may, in this context, comprise a siphon 9, a valve 10 for degassing and a pressure regulator 11, but is not restricted to such a removal unit. Such a siphon in the removal unit for the solid and/or liquid reaction products of the combustion of metal M with the fuel gas, optionally in conjunction with a supply pressure regulator suitable for the particular operating pressure, may be used, for example, in order to enable an elevated or high operating pressure.

The removal unit for the mixture of offgas and carrier gas may, in particular embodiments, also comprise a separation apparatus for the offgas and carrier gas and/or individual components of the offgas.

In particular embodiments, the removal unit for a mixture of offgas and carrier gas may be connected to the feed unit for carrier gas and/or the feed unit for fuel gas in such a way that the mixture of offgas and carrier gas is fed at least partly to the reactor as carrier gas and/or to the burner as fuel gas. The proportion of recycled gas here may be 10% by volume or more, preferably 50% by volume or more, further preferably 60% by volume or more, even further preferably 70% by volume or more, and even more preferably 80% by volume or more, based on the total volume of carrier gas and offgas. In particular embodiments, recycling of the mixture of offgas and carrier gas can be effected to an extent of 90% by volume or more, based on the total volume of carrier gas and offgas.

In particular embodiments, an apparatus of the invention may additionally further comprise at least one boiler and/or at least one heat exchanger and/or at least one gas turbine and/or at least one expander turbine present in the reactor and/or the removal unit for the mixture of offgas and carrier gas. It is thus possible, for example, in the apparatus of FIG. 1 comprising a cyclone reactor 6, for one or more heat exchangers and/or boilers and/or gas turbines and/or expander turbines, which are not shown, to be provided in the reactor 6, in the removal unit 8 and/or in a unit connected to the removal unit 8. It is also possible for heat exchange to take place in the cyclone reactor 6 itself, for example at the outer walls in the reaction region 20 a and/or the separation region 20 b, or else optionally in the region of the expansion chamber 20 c, in which case the corresponding heat exchangers can also be connected to turbines for power generation in generators.

The offgases can thus, as a mixture with carrier gas, be sent to a further use, for example heating of a boiler for steam raising, release of heat in a heat exchanger, operation of a turbine, etc.

If it is not possible to find a suitable heat exchanger by means of which, for example, air with appropriate pressure is then heated and guided into the gas turbine as replacement for the offgas, it is possible to use a boiler, for example. The route using a boiler may be more promising in particular embodiments and is also technically simpler, since it is implementable at lower temperatures and only elevated pressure.

With the aid of one or more heat exchangers and/or one or more boilers, it is then subsequently possible to generate electrical energy, for example through use of a steam turbine and a generator. Alternatively, it is possible that the mixture of offgas and carrier gas is guided directly to a turbine, for example a gas turbine or expander turbine, in order thus to directly generate power. However, this requires very good removal of solids and/or liquid reaction products from the combustion of metal M and fuel gas, as can be provided in accordance with the invention, especially using a grid in the reactor. The selection of whether a boiler or a heat exchanger is used may also depend, for example, on whether solid or liquid reaction products are formed, but may also depend on the plant. In the case of liquid reaction products, for example liquid Li₂CO₃, it is possible, for example, for the reactor wall to function as heat exchanger, whereas, in the case of solid products that form, special heat exchangers may be required. In the case of a corresponding separation of the mixture of offgas and carrier gas from the solid and/or liquid reaction products, direct guiding of the mixture of offgas and carrier gas to a turbine may also be possible, such that it may then be the case here too that no heat exchangers and/or boilers are required in the offgas stream.

In particular embodiments, an apparatus of the invention may comprise a withdrawal apparatus in the removal unit for the mixture of offgas and carrier gas, which is designed to remove a portion of the mixture of offgas and carrier gas in the case of recycling of the mixture of offgas and carrier gas to the feed unit for carrier gas and/or the feed unit for fuel gas through connection of the removal unit for the mixture of offgas and carrier gas to the feed unit for carrier gas and/or the feed unit for fuel gas. Such a portion may, for example, be more than 1% by volume, preferably 5% by volume or more and further preferably 10% by volume or more, based on the total volume of the mixture of offgas and carrier gas. In addition, in particular embodiments, not more than 50% by volume, preferably 40% by volume or less, further preferably 30% by volume or less, more preferably 20% by volume or less, based on the total volume of the mixture of offgas and carrier gas, may be removed from the recycled mixture of offgas and carrier gas. The gas withdrawn may then be available, for example, as product of value for further reactions, for example when carbon monoxide is discharged and then converted in a Fischer-Tropsch process to higher-value hydrocarbons.

It is also possible for the solids removed to be converted further to substances of value. For example, metal nitride prepared from combustion with nitrogen can be converted by hydrolysis with water to ammonia and alkali, in which case the alkali formed can also serve as scavenger for carbon dioxide and/or sulfur dioxide.

In a further aspect, the present invention additionally relates to the use of a pore burner comprising a porous tube as burner for combustion of a metal M selected from alkali metals, alkaline earth metals, aluminum and zinc, and alloys and/or mixtures thereof, with a fuel gas.

The above embodiments, configurations and developments can, if viable, be combined with one another as desired. Further possible configurations, developments and implementations of the invention also include combinations of features of the invention that have been described above or are described hereinafter with reference to the working examples but have not been mentioned explicitly. More particularly, the person skilled in the art will also add individual aspects as improvements or additions to the respective base form of the present invention.

The invention will now be illustrated on the basis of illustrative embodiments which do not restrict the invention in any way.

In an illustrative embodiment, the metal M, for example lithium, is used in liquid form, i.e. above the melting point, for lithium 180° C. The liquid metal M, for example lithium, can be introduced into the pore burner and then reacts directly, optionally after ignition to start the reaction, with the particular fuel gas, for example air, oxygen, carbon dioxide, sulfur dioxide, hydrogen, water vapor, nitrogen oxides NO_(x) such as dinitrogen monoxide, or nitrogen. The combustion of the metal M, for example lithium, can be effected in the apparatus shown in FIG. 1, for example with more than the stoichiometric amount of the fuel gas, in order not to generate excessively high offgas temperatures. Alternatively, the fuel gas can be added in a stoichiometric or substoichiometric amount compared to the metal M. After the combustion, a carrier gas (for example nitrogen, air, carbon monoxide, carbon dioxide and ammonia), which may also correspond to the fuel gas, is added for dilution, in order to reduce the temperature and in order to generate a cyclone for deposition of the solid or liquid reaction products. The hot offgas stream can then be used to heat a boiler or for heat transfer in a heat exchanger or the like.

In a second illustrative embodiment, the fuel gas used may be carbon dioxide and the carrier gas used may be carbon monoxide in the apparatus shown in FIG. 1. The metal M used is, for example, lithium, for example in liquid form, i.e. above the melting point of 180° C. The liquid lithium is introduced into the pore burner 3 and then reacts directly with the fuel gas. It may be the case that electrical ignition or an additional ignition burner are required.

The reaction proceeds according to the following equation:

2Li+2CO₂→Li₂CO₃+CO

The combustion of the lithium is effected in the pore burner 3, preferably with the amount of carbon dioxide required in stoichiometric terms, although it is also possible to choose a slightly super- or substoichiometric ratio (e.g. 0.95:1 to 1:0.95 for the ratio of CO₂:Li). In the case of use of a very high deficiency of carbon dioxide, it is possible, for example, for lithium carbide to form, from which acetylene can then be obtained. In the second step, in the middle portion of the reactor/furnace 6, in the region 4′, the combustion products are mixed with the carbon monoxide carrier gas which is blown into the reactor 6 by nozzles 5. This gives rise to a cyclone, the effect of which is that the solid and/or liquid reaction products are vortexed at the reactor wall and are deposited primarily there. Preferably, an excess of carrier gas is used in order to ensure that the heat that arises through the combustion is transported away sufficiently. As a result, it is possible to suitably adjust the temperature in the reactor 6.

For combustion in pure carbon dioxide, the lithium carbonate that forms has a melting point of 723° C. If the combustion temperature of the reaction products is kept above at least 723° C. by mixing in carrier gas and/or fuel gas through the feed units 1, 5, liquid reaction products can be expected for the combustion. The feed units can be used here for cooling in the strongly exothermic reaction, in order that the plant does not heat up too much, and the lower temperature limit may be the melting point of the salts formed, lithium carbonate here. If the cyclone is additionally operated with gases other than carbon dioxide, for example air or nitrogen for further gases, it is also possible for lithium oxide (melting point m.p. 1570° C.) or lithium nitride (m.p. 813° C.) to form in the reaction products. After separation of the liquid and solid reaction products, which can be improved by means of a grid 6′, the mixture of offgas and carrier gas is guided, for example, into a boiler and utilized for evaporation of water, in order then to drive a steam turbine with downstream generator or to operate other technical apparatuses (for example heat exchangers). The mixture of offgas and carrier gas cooled down by this process can then, for example, be utilized again as carrier gas to generate the cyclone in the furnace. Thus, the residual heat from the offgas after the evaporation process is utilized in the boiler, and only the amount of carbon dioxide needed in stoichiometric terms for the combustion with Li has to be obtained by offgas cleaning, for example in coal-fired power plants.

Table 1 shows the correlation of offgas temperature and stoichiometric excess for the combustion of lithium in pure carbon dioxide, the calculation having been effected with non-temperature-dependent specific heats.

TABLE 1 Operation of the furnace with carbon dioxide as fuel gas and as carrier gas Temperature Excess of fuel gas as a Proportion of CO in the factor, based on the in the offgas offgas mass of fuel gas [Gew. %] 1400° C. 8.0 12.5% 1200° C. 9.8 10.2%  800° C. 15.8 6.3%

In particular embodiments, the combustion can be effected with a certain excess of fuel gas, for example in a molar ratio of fuel gas to metal M of more than 1.01:1, preferably more than 1.05:1, further preferably 5:1 or more, even further preferably 10:1 or more, for example even 100:1 or more, in order to stabilize the offgas temperature within a particular temperature range, and it is possible to add further fuel gas or carrier gas for absorption of heat by means of a cyclone as well as the addition of fuel gas and the inflow of the metal M, for example lithium, in an arrangement of nozzles, as shown in FIG. 1 and FIG. 4. The offgas temperature, in particular embodiments, in the different combustion processes, can be controlled via the excess of gas, such that it may be higher than the melting temperature of the reaction products or mixture thereof (table 1).

With a recirculation of the offgas cooled by the downstream process step, it is possible to enrich carbon monoxide in the offgas. It is possible in particular embodiments to withdraw a proportion from the offgas, and hence to obtain a gas mixture of carbon monoxide and carbon dioxide having a significantly higher proportion of carbon monoxide than specified in table 1. A subsequent separation of gas can purify the carbon monoxide to remove carbon dioxide, and the carbon dioxide can be used further in the circulation or in the burner.

By recycling of the CO product gas, it is possible to lower the combustion temperature in the furnace. In the case of stoichiometric combustion, gas temperatures of more than 3000 K can be achieved, which would lead to material problems. Lowering of the combustion temperature would also be possible by means of an excess of CO₂. However, this excess would have to be about 16 times higher than the stoichiometric amount, and so the CO product gas would have to be highly diluted in the excess of CO₂ (concentration only about 6% by volume). Therefore, it is sensible in particular embodiments to recycle a portion of the CO product gas into the burner and use it as thermal ballast for lowering the temperature. Preference is given here to establishing a particular reaction temperature by recycling a constant amount of offgas and carrier gas mixture as carrier gas. In this case, there is no formation of a CO/CO₂ mixture which has to be separated in a complex manner. The product gas consists mainly of CO and only of small impurities of CO₂. In the steady state, the majority of the CO is circulated and the amount of CO removed from the circuit is just as much as is reformed by the reaction of CO₂ and Li. For example, such a circuit may arise when CO is used as carrier gas in a ratio of 90% by volume or more, based on the mixture of offgas and carrier gas. A suitable amount of carbon dioxide can thus be supplied constantly to the combustion process, whereas a corresponding amount of carbon monoxide can be withdrawn constantly from the circuit as product of value. A corresponding reaction regime is also shown by way of example in FIG. 5. Carbon dioxide is separated from an offgas 100, for example from a combustion power plant such as a coal-fired power plant, in a CO₂ removal 101, and then it is combusted with lithium in step 102, using CO as carrier gas. This forms Li₂CO₃ 103, and a mixture of offgas and carrier gas comprising CO₂ and CO, optionally after a separation 104, can be passed through a boiler 105, with the aid of which a steam turbine 106 and hence a generator 107 are operated. There is recycling of offgas 108 as carrier gas, it being possible to discharge CO in the step 109.

In a third illustrative embodiment, the fuel gas and carrier gas used may be nitrogen in the apparatus shown in FIG. 1. The metal used is, for example, lithium, for example in liquid form, i.e. above the melting point of 180° C. The liquid lithium can be fed to the pore burner 3 and then reacts directly with the fuel gas. It may be the case that electrical ignition or an additional ignition burner are required.

The combustion of the lithium is effected in the pore burner 3, with the amount of nitrogen required in stoichiometric terms, although it is also possible to choose a slightly super- or substoichiometric ratio (e.g. 0.95:1 to 1:0.95 for the ratio of N₂ : Li).

The reaction here is as follows:

6Li+N₂→2Li₃N

In the second step, in the middle portion of the reactor 6, the combustion products are mixed with the carrier gas, for example nitrogen, which is blown into the reactor 6 through the nozzles 5. This gives rise to a cyclone, the effect of which is that the solid and liquid reaction products are vortexed at the reactor wall and are deposited primarily there. For combustion in pure nitrogen, lithium nitride that forms has a melting point of 813 ° C. If the combustion temperature of the reaction products is kept above at least 813 ° C. by mixing in carrier gas and/or fuel gas through the feed units 1, 5, liquid reaction products can be expected for the combustion. The feed units can be used here for cooling in the strongly exothermic reaction, in order that the plant does not heat up too much, and the lower temperature limit may be the melting point of the salts formed, lithium nitride here. If the cyclone is operated with gases other than nitrogen, for example air or carbon dioxide or further gases, it is also possible for lithium oxide (m.p. 1570° C.) or lithium carbonate (m.p. 723° C.) to form in the reaction products. After separation of the liquid and/or solid reaction products, which can be improved by means of a grid 6′, the offgas is guided, for example, into a boiler and utilized for evaporation of water, in order then to drive a turbine with downstream generator or to operate other technical apparatuses (for example heat exchangers). The offgas cooled after this process can then, for example, be utilized again to generate the cyclone in the reactor 6. Thus, the residual heat from the offgas after the evaporation process is utilized in the boiler, and only the amount of nitrogen needed in stoichiometric terms for the combustion has to be obtained, for example by fractionation of air.

Table 2 shows the correlation of offgas temperature and stoichiometric excess for the combustion of lithium in pure nitrogen, the calculation having been effected with non-temperature-dependent specific heats.

TABLE 2 Operation of the furnace with nitrogen as fuel gas and as carrier gas Excess of fuel gas as a factor, based on the mass of Temperature in the offgas fuel gas 1600° C. 5.6 1400° C. 8.5 1200° C. 10.2 1000° C. 13.3  800° C. 16.1  600° C. 18.5

In particular embodiments, the combustion can be effected with a certain excess of fuel gas, for example in a molar ratio of fuel gas to metal M of more than 1.01:1, preferably more than 1.05:1, further preferably 5:1 or more, even further preferably 10:1 or more, for example even 100:1 or more, in order to stabilize the offgas temperature within a particular temperature range, and it is possible to add further fuel gas or carrier gas for absorption of heat by means of a cyclone as well as the addition of fuel gas and the inflow of the metal M, for example lithium, in an arrangement of nozzles, as shown in FIG. 1 and FIG. 4. The offgas temperature, in particular embodiments, in the different combustion processes, can be controlled via the excess of gas, such that it may be higher than the melting temperature of the reaction products or mixture thereof (table 2).

A corresponding reaction regime is also shown by way of example in FIG. 6. Nitrogen is separated from the air 200 in an airfractionation 201 and then combusted with the lithium in step 202, using nitrogen, for example likewise from the air fractionation 201, as carrier gas. This forms Li₂N₃ 203, and the mixture of offgas and carrier gas comprising N₂ 204 can be guided through a boiler 205, with the aid of which a steam turbine 206 and hence a generator 207 are operated. There is recycling of offgas 208 as carrier gas. Ammonia 210 can be obtained from the lithium nitride 203 by hydrolysis 209, forming LiOH 211 which can be reacted with carbon dioxide to give lithium carbonate 212.

In a fourth illustrative embodiment, it may also be possible, for example in the case of use of air as fuel gas, to use two reactors, for example two cyclone reactors, connected in series, in which case, in the first cyclone reactor, the metal M, for example lithium, and the oxygen from the air can be used to produce metal oxide, for example Li₂O, and the offgas contains primarily nitrogen, and this offgas can then react in a second cyclone reactor as fuel gas with metal M, for example lithium, to give metal nitride, for example Li₃N. In this case, for example, nitrogen can function as carrier gas, which can also be obtained from the first offgas, or the first offgas itself if it is being circulated, for example.

Through the construction of the apparatus of the invention, especially through the use of porous combustion tubes, it is possible to separate the solid or liquid reaction products or mixtures thereof in a simple manner from the offgases formed, and hence to send the offgases to a use in, for example, a gas turbine or expander turbine, a heat exchanger, or a boiler. In this way, in addition, the entire combustion apparatus can also be made more compact and the combustion can be configured so as to be gentler in respect of the apparatus through localization of the combustion process.

In addition, the apparatus, for example a reactor such as a furnace, can be run at elevated operating pressure, and thus the combustion and deposition process can be matched to the respective conditions of the downstream step. The possibility of distinction of fuel gas and carrier gas for establishment of a cyclone, in particular embodiments, enables the recycling of offgases after the release of heat. Recirculation is easily possible with this construction. Gas mixtures are also possible as fuel gas and carrier gas. By recycling of the offgas after the process step(s), it is possible to save energy and material. 

What is claimed is:
 1. A process for combusting a metal M selected from the group consisting of alkali metals, alkaline earth metals, aluminium, zinc, alloys or mixtures thereof with a fuel gas, the method comprising: supplying the metal M in liquid form in the interior of a pore burner comprising a porous tube a burner; And guiding the fuel gas onto an outer surfaces of the pore burner and combusting the fuel gas with the metal M. 2-3. (canceled)
 4. The process of claim 1, wherein the combustion occurs at a temperature above the melting point of salts formed in the reaction of the metal M and the fuel gas.
 5. The process of claim 1, wherein the metal M is supplied as an alloy of at least two metals M.
 6. The process of claim 1, comprising separating reaction products of the combustion after the combustion.
 7. The process of claim 6, comprising using a cyclone to effect the separation of the reaction products.
 8. The process of claim 1, further comprising using reaction products of the combustion to generate energy using at least one or an expander turbine, a gas turbine, a heat exchanger, or a boiler.
 9. An apparatus for combustion of a metal M selected from the group consisting of alkali metals, alkaline earth metals, aluminum and zinc, and alloys or mixtures thereof with a fuel gas, the apparatus comprising: a pore burner comprising a porous tube as a burner, a metal feed unit configured to feed the metal M, in liquid form, to the pore burner, and a fuel gas feed unit configured to supply at least a portion of the fuel gas to an outer surfaces of the pore burner.
 10. (canceled)
 11. The apparatus of claim 9, wherein the pore burner is arranged such that reaction products of the combustion of the metal with the fuel gas are removed by gravity from the surface of the pore burner.
 12. The apparatus of claim 9, wherein the pore burner is formed from a material selected from the group consisting of iron, chromium, nickel, niobium, tantalum, molybdenum, tungsten, zirconium, alloys of these metals, stainless steel, and chromium-nickel steel.
 13. The apparatus of claim 9, further comprising a separation unit configured to separate combustion products of the metal M and the fuel gas, wherein separation unit comprises a cyclone reactor.
 14. The apparatus of claim 9, further comprising at least one of an expander turbine, a gas turbine, a heat exchanger, or a boiler.
 15. (canceled)
 16. The apparatus of claim 9, further comprising a heating apparatus configured to liquefy the metal M before being fed to the pore burner. 